Because of its high thermal conductivity, the application of aluminum nitride to electronic industry materials, such as electrical substrates having high thermal conductivity and heat radiating parts, has become of great interest.
Conventional processes for producing aluminum nitride powder include those disclosed, for example, in JP-A-61-178409 and JP-A-60-176910 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). According to the former method, a resin powder comprising nitrogen atoms is added to a powder mixture of alumina and carbon, and the resulting mixture is subjected to reduction nitridation to produce aluminum nitride free from alumina and aluminum oxynitride. The latter discloses a method in which the alumina powder is previously brought into contact with a solution of an organic compound which would give carbon under the reaction conditions.
There remains, however, problems in the above described methods. JP-A-61-178409 describes that the purpose of mixing the resin powder is to give highly pure aluminum nitride free from alumina and aluminum oxynitride. To this end, the resin to be used necessarily contains nitrogen atoms. This method, however, is not suitable for the production of fine aluminum nitride having excellent sinterability capable of effecting reaction at high rate. The method disclosed in JP-A-60-176910 uses organic polymers in solution, therefore, the organic polymers to are employed be dissolved in a solvent such as water, ethanol, acetone, and ether. This requires additional steps such as drying or carbonization prior to the nitridation reduction, resulting in complicated operation which is unfavorable from the economical viewpoint and also from the safety viewpoint. Moreover, it is necessary to maintain the reaction system at a high temperature for a long time to complete the reaction.